First output position calculation method, storage medium, positioning device, and electronic instrument

ABSTRACT

In the first positioning, a positioning process that calculates the present position based on acquired GPS satellite signals (step A 3 ) is performed a plurality of times. A number of times that the difference (position difference) ΔP between the calculated present located position and the preceding located position is successively equal to or less than a given value is counted using a position counter, and a number of times that the difference (time difference) ΔT between the present time error and the preceding time error is successively equal to or less than a given value is counted using a time counter each time the positioning process is performed (step A 5 ). A position threshold value and a time threshold value are determined by changing a reference threshold value by an amount corresponding to an APR average value (step A 7 ). When the position count value has reached the position threshold value (step A 9 : YES) and the time count value has reached the time threshold value (step A 11 : YES), the present position is determined to be the first located position and output (step A 13 ).

Japanese Patent Application No. 2007-101477 filed on Apr. 9, 2007 andJapanese Patent Application No. 2008-37115 filed on Feb. 19, 2008, arehereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a first output position calculationmethod, a storage medium, a positioning device, and an electronicinstrument.

The global positioning system (GPS) is widely known as a satellitepositioning system, and is utilized for a car navigation system and thelike. In the GPS, GPS satellite signals are respectively transmittedfrom a plurality of GPS satellites which orbit the earth, and a GPSreceiver calculates (locates) its present position based on the receivedGPS satellite signals.

A GPS satellite signal affected by a multipath or the like may beincluded in the acquired GPS satellite signals. The term “multipath”refers to a phenomenon in which an indirect wave reflected or diffractedby a building or topography is superimposed on a direct wave from a GPSsatellite so that the GPS receiver receives identical radio wavesthrough multiple paths. Such a reception environment is referred to as amultipath environment. The present position may not be accuratelycalculated (located) when using a GPS satellite signal affected by amultipath. Specifically, it is necessary to perform positioningcalculations while excluding a GPS satellite signal affected by amultipath or the like from the acquired GPS satellite signals. As amethod of determining a GPS satellite signal affected by a multipath orthe like, a method using an a priori residual (APR) has been known (seeJP-A-2003-240836, for example).

A GPS receiver repeats positioning calculations each time a given periodof time (e.g., one second) has elapsed, and outputs the calculatedpresent position of the GPS receiver as the positioning result. Aboutseveral seconds are normally required to output the first positioningresult after starting positioning. A time to first fix (TTFF; timerequired to output the first positioning result) and positioningaccuracy have a relationship in which the positioning accuracy decreaseswhen giving priority to a reduction in TTFF and the TTFF increases whengiving priority to an increase in positioning accuracy. Whether to givepriority to an increase in positioning accuracy or a reduction in TTFFis determined depending on the reception environment. For example, it isdesirable to give priority to an increase in positioning accuracy over areduction in TTFF in a reception environment (e.g., multipathenvironment) with poor positioning accuracy so that the positioningresult is output after the Z-count has been decoded and the positioningaccuracy has been improved, even if the TTFF increases. On the otherhand, priority may be given to a reduction in TTFF in an open-skyenvironment with high positioning accuracy so that the positioningresult is output without waiting for the Z-count to be decoded.

SUMMARY

According to one aspect of the invention, there is provided a firstoutput position calculation method comprising:

selecting satellite sets, each of the satellite sets being a combinationof satellites used for a present positioning process;

calculating present position candidates corresponding to the respectivesatellite sets using satellite signals from the satellites included inthe respective satellite sets;

calculating APR values of the satellites of the respective satellitesets based on the present position candidates;

calculating an APR average value of the present positioning process byaveraging the APR values of the respective satellite sets;

selecting a present position candidate from the present positioncandidates corresponding to the respective satellite sets anddetermining the selected present position candidate to be a locatedposition determined by the present positioning process;

changing a repetitive execution count of the positioning process basedon the APR average value; and

determining a final located position calculated when the positioningprocess has been executed in a number corresponding to the repetitiveexecution count to be a first located position to be output.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is an internal configuration diagram of a portable telephone.

FIGS. 2A and 2B show examples of experimental results indicating therelationship between an APR average value and a positioning error.

FIG. 3 is a configuration diagram of a ROM.

FIG. 4 shows a data configuration example of a count-up condition table.

FIG. 5 shows a data configuration example of a threshold value changecondition table.

FIG. 6 is a configuration diagram of a RAM.

FIG. 7 shows a data configuration example of satellite position data.

FIG. 8 shows a data configuration example of satellite set data.

FIG. 9 shows a data configuration example of positioning result data.

FIG. 10 is a flowchart of a baseband process.

FIG. 11 is a flowchart of a positioning calculation process executedduring the baseband process.

FIG. 12 is a flowchart of a count process executed during the basebandprocess.

FIG. 13 is a flowchart of a threshold value change process executedduring the baseband process.

DETAILED DESCRIPTION OF THE EMBODIMENT

Several embodiments of the invention may enable whether to give priorityto an increase in positioning accuracy or a reduction in TTFF to beappropriately determined depending on the reception environment whenoutputting the first positioning result.

According to one embodiment of the invention, there is provided a firstoutput position calculation method that calculates a first locatedposition to be output after starting positioning when receivingsatellite signals transmitted from positioning satellites and performingpresent position positioning calculations based on the receivedsatellite signals, the method comprising:

executing a positioning process that performs positioning calculationsbased on the received satellite signals to calculate a located position;

changing a repetitive execution count of the positioning process; and

determining a final located position calculated when the positioningprocess has been executed in a number corresponding to the repetitiveexecution count to be a first located position to be output,

the executing of the positioning process including:

selecting satellite sets based on the received satellite signals, eachof the satellite sets being a combination of satellites used for apresent positioning process;

calculating present position candidates corresponding to the respectiveselected satellite sets using the satellite signals from the satellitesincluded in the respective selected satellite sets;

calculating APR values of the respective selected satellite sets, theAPR value being the sum of the square of the difference between 1) apseudo-range and 2) an approximate distance of a target satellite of atarget satellite set, the approximate distance being a distance betweenthe target satellite and the present position candidate of the targetsatellite set;

calculating an APR average value of the present positioning process byaveraging the APR values of the respective satellite sets;

selecting a present position candidate from the present positioncandidates corresponding to the respective satellite sets anddetermining the selected present position candidate to be a locatedposition determined by the present positioning process; and

the changing of the repetitive execution count including changing therepetitive execution count based on the APR average value.

According to another embodiment of the invention, there is provided apositioning device that receives satellite signals transmitted frompositioning satellites and performs present position positioningcalculations based on the received satellite signals, the positioningdevice comprising:

a positioning section that executes a positioning process that performspositioning calculations based on the received satellite signals tocalculate a located position;

a repetitive execution count change section that changes a repetitiveexecution count of the positioning process; and

a first output position determination section that determines a finallocated position calculated when the positioning section has executedthe positioning process in a number corresponding to the repetitiveexecution count to be the first located position,

the positioning section including:

a satellite set selection section that selects satellite sets based onthe received satellite signals, each of the satellite sets being acombination of satellites used for a present positioning process;

a present position candidate calculation section that calculates presentposition candidates corresponding to the respective selected satellitesets using the satellite signals from the satellites included in therespective selected satellite sets;

an APR value calculation section that calculates APR values of therespective selected satellite sets, the APR value being the sum of thesquare of the difference between 1) a pseudo-range and 2) an approximatedistance of a target satellite of a target satellite set, theapproximate distance being a distance between the target satellite andthe present position candidate of the target satellite set; an averagevalue calculation section that calculates an APR average value of thepresent positioning process by averaging the APR values of therespective satellite sets; and

a present located position selection section that selects a presentposition candidate from the present position candidates corresponding tothe respective satellite sets and determining the selected presentposition candidate to be a located position determined by the presentpositioning process; and

the repetitive execution count change section including an APR averagevalue reference count change section that changes the repetitiveexecution count based on the APR average value calculated by thepositioning section.

According to the above configuration, the final located positioncalculated when the positioning process that calculates the locatedposition has been executed in a number corresponding to the repetitiveexecution count is determined to be the first located position to beoutput. The repetitive execution count is changed based on the APRaverage value.

The APR value of the satellite set is calculated according to anequation (1) described later based on a pseudo-range ym and anapproximate distance yp of each satellite included in the satellite set.The approximate distance yp of each satellite is calculated according toan equation (2) described later based on the position (Xi, Yi, Zi) ofthat satellite and the present position (x, y, z) calculated based onthe satellite signal from each satellite included in the targetsatellite set.

The APR value and a positioning error have a relationship in which thepositioning accuracy of the satellite set decreases as the APR valueincreases. A satellite signal affected by a multipath or the like ismore likely included in the received satellite signals (i.e., multipathenvironment) as the APR average value increases. Specifically, thereception environment can be determined from the APR average value.Therefore, the TTFF required to output the first located position can bereduced corresponding to the reception environment by changing therepetitive execution count based on the APR average value. For example,the reception environment is likely to be the multipath environment(i.e., positioning accuracy is low) when the APR average value is large.In this case, priority is given to an increase in positioning accuracyby increasing the repetitive execution count. On the other hand, thereception environment is likely to be the open-sky environment (i.e.,positioning accuracy is high) when the APR average value is small. Inthis case, priority is given to a reduction in TTFF by decreasing therepetitive execution count.

According to another embodiment of the invention, there is provided afirst output position calculation method comprising:

selecting satellite sets, each of the satellite sets being a combinationof satellites used for a present positioning process;

calculating present position candidates corresponding to the respectivesatellite sets using satellite signals from the satellites included inthe respective satellite sets;

calculating APR values of the satellites of the respective satellitesets based on the present position candidates;

calculating an APR average value of the present positioning process byaveraging the APR values of the respective satellite sets;

selecting a present position candidate from the present positioncandidates corresponding to the respective satellite sets anddetermining the selected present position candidate to be a locatedposition determined by the present positioning process;

changing a repetitive execution count of the positioning process basedon the APR average value; and

determining a final located position calculated when the positioningprocess has been executed in a number corresponding to the repetitiveexecution count to be a first located position to be output.

According to another embodiment of the invention, there is provided apositioning device comprising:

a satellite set selection section that selects satellite sets, each ofthe satellite sets being a combination of satellites used for a presentpositioning process;

a present position candidate calculation section that calculates presentposition candidates corresponding to the respective satellite sets usingsatellite signals from the satellites included in the respectivesatellite sets;

an APR value calculation section that calculates APR values of thesatellites of the respective satellite sets based on the presentposition candidates;

an average value calculation section that calculates an APR averagevalue of the present positioning process by averaging the APR values ofthe respective satellite sets;

a present located position selection section that selects a presentposition candidate from the present position candidates corresponding tothe respective satellite sets and determines the selected presentposition candidate to be a located position determined by the presentpositioning process;

an APR average value reference count change section that changes arepetitive execution count of the positioning process based on the APRaverage value; and

a first output position determination section that determines a finallocated position calculated when the positioning process has beenexecuted in a number corresponding to the repetitive execution count tobe a first located position to be output.

In the first output position calculation method,

the changing of the repetitive execution count may include changing therepetitive execution count based on the APR average value calculated bythe present positioning process each time the positioning process isexecuted.

In the positioning device,

the repetitive execution count change section may change the repetitiveexecution count based on the APR average value calculated by the presentpositioning process each time the positioning section executes thepositioning process.

According to the above configuration, the repetitive execution count ischanged based on the APR average value calculated by the presentpositioning process each time the positioning process is executed. TheAPR average value changes each time the positioning process is executed.Therefore, the repetitive execution count can be more appropriatelydetermined by changing the repetitive execution count based on the APRaverage value calculated by the present positioning process each timethe positioning process is executed.

The first output position calculation method may further includeresetting and counting the repetitive execution count again when thedifference between the located position determined by the precedingpositioning process and the located position determined by the presentpositioning process does not satisfy a given short distance condition,and successively counting the repetitive execution count when thedifference between the located position determined by the precedingpositioning process and the located position determined by the presentpositioning process satisfies the given short distance condition.

The positioning device may further include a repetitive execution countcounting section that resets and counts the repetitive execution countagain when the difference between the located position determined by thepreceding positioning process and the located position determined by thepresent positioning process does not satisfy a given short distancecondition, and successively counts the repetitive execution count whenthe difference between the located position determined by the precedingpositioning process and the located position determined by the presentpositioning process satisfies the given short distance condition.

According to the above configuration, the repetitive execution count isreset and counted again when the difference between the located positiondetermined by the preceding positioning process and the located positiondetermined by the present positioning process does not satisfy the givenshort distance condition, and is successively counted when thedifference between the located position determined by the precedingpositioning process and the located position determined by the presentpositioning process satisfies the given short distance condition.Specifically, the first located position is output when the number oftimes that the difference in located position successively satisfies theshort distance condition has reached the repetitive execution count.Therefore, the first located position to be output is determined when avariation in located position has decreased in time series.

In the first output position calculation method,

the calculating of the present position candidate may includecalculating a time error using the satellite signals from the satellitesincluded in the target satellite set;

the executing of the positioning process may include determining thetime error calculated when calculating the present position candidate tobe a time error determined by the present positioning process; and

the method may further include resetting and counting the repetitiveexecution count again when the difference between the time errordetermined by the preceding positioning process and the time errordetermined by the present positioning process does not satisfy a givenapproximation condition, and successively counting the repetitiveexecution count when the difference between the time error determined bythe preceding positioning process and the time error determined by thepresent positioning process satisfies the given approximation condition.

In the positioning device,

the present position candidate calculation section may calculate a timeerror using the satellite signals from the satellites included in thetarget satellite set;

the positioning section may include a present time error determinationsection that determines the time error calculated when the presentposition candidate selected by the present located position selectionsection has been calculated by the present position candidatecalculation section to be a time error determined by the presentpositioning process; and

the positioning device may further include a repetitive execution countcounting section that resets and counts the repetitive execution countagain when the difference between the time error determined by thepreceding positioning process and the time error determined by thepresent positioning process does not satisfy a given approximationcondition, and successively counts the repetitive execution count whenthe difference between the time error determined by the precedingpositioning process and the time error determined by the presentpositioning process satisfies the given approximation condition.

According to the above configuration, the time error is calculated usingthe satellite signals from the satellites included in the targetsatellite set when calculating the present position candidate, and therepetitive execution count is reset and counted again when thedifference between the time error determined by the precedingpositioning process and the time error determined by the presentpositioning process does not satisfy the given approximation condition,and is successively counted when the difference between the time errordetermined by the preceding positioning process and the time errordetermined by the present positioning process satisfies the givenapproximation condition. Specifically, the first located position isoutput when the number of times that the difference in time errorsuccessively satisfies the approximation condition has reached therepetitive execution count. Therefore, the first located position to beoutput is determined when a variation in time error has decreased intime series.

In the first output position calculation method,

the calculating of the present position candidate may includecalculating a time error using the satellite signals from the satellitesincluded in the target satellite set;

the executing of the positioning process may include determining thetime error calculated when calculating the present position candidateselected as the located position by the present positioning process tobe a time error determined by the present positioning process; and

the method may further include resetting and counting the repetitiveexecution count again when 1) the difference between the locatedposition determined by the preceding positioning process and the locatedposition determined by the present positioning process does not satisfya given short distance condition or 2) the difference between the timeerror determined by the preceding positioning process and the time errordetermined by the present positioning process does not satisfy a givenapproximation condition, and successively counting the repetitiveexecution count when the difference between the located positiondetermined by the preceding positioning process and the located positiondetermined by the present positioning process satisfies the given shortdistance condition and the difference between the time error determinedby the preceding positioning process and the time error determined bythe present positioning process satisfies the given approximationcondition.

In the positioning device,

the present position candidate calculation section may calculate a timeerror using the satellite signals from the satellites included in thetarget satellite set;

the positioning section may include present time error determinationsection that determines the time error calculated when the presentposition candidate selected by the present located position selectionsection has been calculated by the present position candidatecalculation section to be a time error determined by the presentpositioning process; and

the positioning device may further include a repetitive execution countcounting section that resets and counts the repetitive execution countagain when 1) the difference between the located position determined bythe preceding positioning process and the located position determined bythe present positioning process does not satisfy a given short distancecondition or 2) the difference between the time error determined by thepreceding positioning process and the time error determined by thepresent positioning process does not satisfy a given approximationcondition, and successively counts the repetitive execution count whenthe difference between the located position determined by the precedingpositioning process and the located position determined by the presentpositioning process satisfies the given short distance condition and thedifference between the time error determined by the precedingpositioning process and the time error determined by the presentpositioning process satisfies the given approximation condition.

According to the above configuration, the time error is calculated usingthe satellite signals from the satellites included in the targetsatellite set when calculating the present position candidate, and therepetitive execution count is reset and counted again when 1) thedifference between the located position determined by the precedingpositioning process and the located position determined by the presentpositioning process does not satisfy the given short distance conditionor 2) the difference between the time error determined by the precedingpositioning process and the time error determined by the presentpositioning process does not satisfy the given approximation condition.The repetitive execution count is successively counted when thedifference between the located position determined by the precedingpositioning process and the located position determined by the presentpositioning process satisfies the given short distance condition and thedifference between the time error determined by the precedingpositioning process and the time error determined by the presentpositioning process satisfies the given approximation condition.Specifically, the first located position is output when the number oftimes that the difference in the located position successively satisfiesthe short distance condition has reached the repetitive execution countand the number of times that the difference in the time errorsuccessively satisfies the approximation condition has reached therepetitive execution count. Therefore, the first located position to beoutput is determined when variations in located position and time errorin time series have decreased.

Another embodiment of the invention relates to a computer-readablestorage medium storing a program that causes a computer to execute theabove first output position calculation method, the computer beingincluded in a positioning device that receives satellite signalstransmitted from positioning satellites and locates a present positionbased on the received satellite signals.

The term “storage medium” used herein refers to a storage medium (e.g.,hard disk, CD-ROM, DVD, memory card, or IC memory) from whichinformation stored therein can be read by a computer.

A further embodiment of the invention relates to an electronicinstrument comprising the above positioning device.

Preferred embodiments of the invention are described in detail belowwith reference to the drawings.

The following embodiments illustrate specific preferred examples of theinvention, and are provided with various technologically preferredlimitations. Note that the scope of the invention is not limited to thefollowing embodiments unless there is a description which limits theinvention.

An embodiment in which the invention is applied to a portable telephoneis described below with reference to the drawings.

Configuration

FIG. 1 is a block diagram showing the internal configuration of aportable telephone 1 according to this embodiment. As shown in FIG. 1,the portable telephone 1 includes a GPS antenna 10, a GPS receiversection 20 (positioning device), a host central processing unit (CPU)40, an operation section 41, a display section 42, a read-only memory(ROM) 43, a random access memory (RAM) 44, a portable telephone antenna50, and a portable telephone wireless communication circuit section 60.

The GPS antenna 10 is an antenna which receives an RF signal including aGPS satellite signal transmitted from a GPS satellite, and outputs thereceived RF signal.

The GPS receiver section 20 acquires/extracts the GPS satellite signalfrom the RF signal received by the GPS antenna 10, and calculates thepresent position of the portable telephone 1 by performing positioningcalculations based on a navigation message and the like extracted fromthe GPS satellite signal. The GPS receiver section 20 includes a radiofrequency (RF) receiver circuit section 21, an oscillation circuit 22,and a baseband process circuit section 30. The RF receiver circuitsection 21 and the baseband process circuit section 30 may be producedas different large scale integrated (LSI) circuits, or may be producedin one chip.

The oscillation circuit 22 is a crystal oscillator or the like whichgenerates and outputs an oscillation signal having a given oscillationfrequency.

The RF receiver circuit section 21 multiplies the RF signal input fromthe GPS antenna 10 by a signal obtained by dividing or multiplying thefrequency of the oscillation signal input from the oscillation circuit22 to down-convert the RF signal into an intermediate-frequency signal(hereinafter referred to as “IF signal”). The RF receiver circuitsection 21 amplifies the IF signal, converts the amplified signal into adigital signal using an A/D converter, and outputs the digital signal,for example.

The baseband process circuit section 30 is a circuit section whichacquires/tracks the GPS satellite signal from the IF signal input fromthe RF receiver circuit section 21, and performs pseudo-rangecalculations, positioning calculations, and the like based on anavigation message, time information, and the like extracted by decodingdata.

Specifically, the baseband process circuit section 30 acquires the GPSsatellite signal based on the input IF signal. The baseband processcircuit section 30 acquires the GPS satellite signal by extracting theGPS satellite signal from the IF signal by performing a correlationprocess on the IF signal. Specifically, the baseband process circuitsection 30 performs a coherent process which calculates the correlationbetween the IF signal and a pseudo-generated C/A code replica (codereplica) using FFT calculations, and an incoherent process whichintegrates the correlation values (i.e., the results of the coherentprocess) to calculate an integrated correlation value. As a result, thephases of the C/A code and a carrier frequency contained in the GPSsatellite signal are obtained.

After acquiring the GPS satellite signal, the baseband process circuitsection 30 tracks the acquired GPS satellite signal. The basebandprocess circuit section 30 tracks the GPS satellite signals bysynchronously holding a plurality of acquired GPS satellite signals inparallel. For example, the baseband process circuit section 30 performsa code loop which is implemented by a delay locked loop (DLL) and tracksthe phase of the C/A code, and a carrier loop which is implemented by aphase locked loop (PLL) and tracks the phase of the carrier frequency.The baseband process circuit section 30 extracts the navigation messageby decoding data contained in each GPS satellite signal which has beentracked, and performs pseudo-range calculations, positioningcalculations, and the like to locate the present position.

The baseband process circuit section 30 includes a CPU 31, a ROM 32, anda RAM 33. The baseband process circuit section 30 also includes variouscircuits such as a C/A code replica generation circuit, a correlationcalculation circuit, and a data decoder circuit.

The CPU 31 controls each section of the baseband process circuit section30 and the RF receiver circuit section 21, and performs variouscalculations including a baseband process described later.

In the baseband process, the CPU 31 decodes the navigation messageincluded in the acquired and tracked GPS satellite signal, andcalculates the present position of the portable telephone 1 based onorbit information and time information of the GPS satellite included inthe decoded navigation message. Specifically, the CPU 31 calculates theposition of each GPS satellite and the pseudo-range between the GPSreceiver and each GPS satellite when the GPS satellite has transmittedthe GPS satellite signal based on the difference between the time atwhich each GPS satellite has transmitted the GPS satellite signal andthe time at which the GPS receiver has received the GPS satellitesignal. The CPU 31 calculates the present position by solvingsimultaneous equations in which the present position and a time errorbetween the GPS satellite and the GPS receiver are unknown quantities.The CPU 31 can calculate the present position by receiving GPS satellitesignals from at least four GPS satellites. This is because thecoordinate values (x,y,z) of the present position (i.e.,three-dimensional position) and a time error T between the GPS satelliteand the GPS receiver are used as unknown quantities.

Specifically, the CPU 31 repeats a positioning process which calculatesa present position P of the portable telephone 1 at given time intervals(e.g., intervals of one second). In the positioning process, the CPU 31selects satellite sets (e.g., combinations of four or more GPSsatellites) based on the acquired GPS satellite signals. For example,when eight GPS satellite signals have been acquired, the CPU 31 selects163 (=8C8+8C7+8C6+8C5+8C4) satellite sets. The CPU 31 then performspositioning calculations corresponding to each selected satellite setusing a least-square method or the like to calculate present positioncandidates of the portable telephone 1 (i.e., present positioncandidates for the position of the portable telephone 1) and time errorcandidates. The CPU 31 selects one satellite set from the satellite setsbased on a given criterion, for example. The CPU 31 determines thepresent position candidate corresponding to the selected satellite setto be the present position P, and determines the time error candidatecorresponding to the selected satellite set to be the present time errorT. As the criterion, a position dilution of precision (PDOP) based onthe constellation of the GPS satellites of the satellite set, or thesignal strength of each GPS satellite signal may be used, for example.Note that about several tens of satellite sets made up of six or moreGPS satellites may be extracted from the satellite sets generated basedon the acquired GPS satellite signals, and the located position and thetime error may be determined based on the extracted satellite sets, forexample.

In this embodiment, the positioning process is repeated one or moretimes immediately after starting positioning (first positioning), andthe present position P calculated by the final positioning process isoutput as the first located position. After the first located positionhas been determined and output, the present position P calculated byeach positioning process is output (positioning output) as the locatedposition.

In the first positioning, when the present position P and the time errorT have been calculated by each positioning process, the difference(position difference) ΔP between the calculated present position P and apresent position P0 calculated by the preceding positioning process iscalculated. When the calculated position difference ΔP satisfies apredetermined short distance condition (e.g., 200 m or less), a positioncounter is incremented (updated) by one. When the calculated positiondifference ΔP does not satisfy the short distance condition, theposition counter is cleared to zero. The position counter has beencleared to zero when starting positioning. Specifically, the count value(position count value) of the position counter indicates the number oftimes that the position difference ΔP has consecutively become equal toor less than a given value.

The difference (time difference) ΔT between the present time error T anda time error T0 calculated by the preceding positioning process is alsocalculated. When the calculated time difference ΔT satisfies apredetermined approximation condition (e.g., 0.02 seconds or less), atime counter is incremented (updated) by one. When the calculated timedifference ΔT does not satisfy the approximation condition, the timecounter is cleared to zero. The time counter has been cleared to zerowhen starting positioning. Specifically, the count value (time countvalue) of the time counter indicates the number of times that the timedifference ΔT has consecutively become equal to or less than a givenvalue.

Also, a position threshold value and a time threshold value aredetermined. Specifically, a predetermined reference threshold value(e.g., “3”) is increased or decreased by an amount corresponding to anAPR average value in the present positioning process to determine theposition threshold value and the time threshold value. The APR averagevalue is the average value of a priori residual (APR) (APR values) ofthe satellite sets selected in the present positioning process.

The count values are respectively compared with the threshold values.When the position count value has reached the position threshold valueand the time count value has reached the time threshold value, thepresent position P is determined to be the first located position and isoutput. When the position count value has not reached the positionthreshold value or the time count value has not reached the timethreshold value, the next positioning process is performed.

The a priori residual (APR) (APR value) of a satellite set is given bythe following equation (1):

$\begin{matrix}{{A\; P\; R} = {\sum\limits_{i}^{N}\left( {{ym}_{i} - {yp}_{i}} \right)^{2}}} & (1)\end{matrix}$

where, N is the number of GPS satellites (number of satellites) includedin the target satellite set, and i (=1, 2, . . . , and N) indicates theith GPS satellite among the GPS satellites included in the targetsatellite set. ymi is the pseudo-range between the ith GPS satellite andthe portable telephone 1. ypi is the distance (approximate distance)between the position (Xi, Yi, Zi) of the ith GPS satellite and thepresent position (x, y, z) of the portable telephone 1 obtained bypositioning calculations, and is given by the following equation (2).

yp _(i)=√{square root over ((X _(i) −x)²+(Y _(i) −y)²+(Z _(i)−z)²)}{square root over ((X _(i) −x)²+(Y _(i) −y)²+(Z _(i) −z)²)}{squareroot over ((X _(i) −x)²+(Y _(i) −y)²+(Z _(i) −z)²)}  (2)

Specifically, the APR value is given as the sum of the square of thedifference between the pseudo-range ym and the approximate distance ypof each GPS satellite of the target satellite set.

FIGS. 2A and 2B show examples of experimental results indicating therelationship between the APR value and positioning accuracy. FIG. 2Ashows experimental results in a multipath environment, and FIG. 2B showsexperimental results in an open-sky environment. The present position ofthe portable telephone 1 is known. FIGS. 2A and 2B show the positioningresults in the multipath environment and the open-sky environment intime series from the start of positioning. A satellite set (selectedsatellite set) selected in the positioning process, an APR averagevalue, and a horizontal error are provided as the positioning results.The term “APR average value” refers to the average value of the APRvalues of the satellite set selected in the positioning process. Theterm “horizontal error” refers to the horizontal difference between theknown position of the portable telephone 1 and the present position Pcalculated by the positioning process. The Z-count is decoded in thefifth positioning process in each reception environment. Specifically,the first to fourth positioning processes are performed before theZ-count is decoded, and the fifth and subsequent positioning processesare performed after the Z-count has been decoded.

As shown in FIGS. 2A and 2B, the larger the APR average value, thelarger the horizontal error (i.e., the lower the positioning accuracy)is.

When comparing the multipath environment and the open-sky environment,the APR value and the horizontal error are larger in the multipathenvironment as compared with the open-sky environment. This means thatthe reception environment can be determined from the APR average value.Specifically, the reception environment is likely to be the multipathenvironment when the APR average value is large, and is likely to be theopen-sky environment when the APR average value is small.

In the multipath environment, the horizontal error is large and variesto a large extent before the Z-count is decoded, but decreases andvaries to a small extent after the Z-count has been decoded. The APRaverage value also decreases accompanying a decrease in horizontal errorafter the Z-count has been decoded. Specifically, it is desirable tooutput the first located position after the Z-count has been decoded inthe multipath environment.

In the open-sky environment, the horizontal error varies to only a smallextent regardless of whether or not the Z-count has been decoded. TheAPR average value also varies to only a small extent regardless ofwhether or not the Z-count has been decoded. Specifically, the firstlocated position may be output before the Z-count is decoded in theopen-sky environment.

In this embodiment, the output timing of the first located position isdetermined based on the relationship between the APR average value andthe positioning accuracy. Specifically, whether or not the variation inthe present position P has decreased is determined depending on whetheror not the position count value has reached the position thresholdvalue, and whether or not the variation in the time error T hasdecreased is determined depending on whether or not the time count valuehas reached the time threshold value. The first located position isoutput at a timing when it has been determined that the variation in thepresent position P and the variation in the time error T have decreased.

The position threshold value and the time threshold value are determinedbased on the APR average value in each positioning process. Therefore,the output timing of the first located position is changed correspondingto the reception environment of the present positioning process evenduring travel. Specifically, when the reception environment is likely tobe the multipath environment (i.e., APR average value is large), theposition threshold value and the time threshold value are increased todelay the output timing of the first located position. When thereception environment is likely to be the open-sky environment (i.e.,APR average value is small), the position threshold value and the timethreshold value are decreased to advance the output timing of the firstlocated position.

Again referring to FIG. 1, the ROM 32 stores a system program whichcauses the CPU 31 to control each section of the baseband processcircuit section 30 and the RF receiver circuit section 21, and a programand data necessary for the CPU 31 to implement various processesincluding the baseband process. FIG. 3 shows an example of theconfiguration of the ROM 32. As shown in FIG. 3, the ROM 32 stores abaseband process program 321, a count-up condition table 322, and athreshold value change condition table 323.

The count-up condition table 322 is a data table which definesconditions whereby the position counter and the time counter areincremented. FIG. 4 shows an example of the data configuration of thecount-up condition table 322. As shown in FIG. 4, the count-up conditiontable 322 stores conditions whereby the count values of the positioncounter and the time counter are incremented. Specifically, a positiondifference ΔP by which the variation in the present position P in eachpositioning process is considered to be small is defined as the shortdistance condition for the position counter. A time difference ΔT bywhich the variation in the time error T in each positioning process isconsidered to be small is defined as the approximation condition for thetime counter.

The threshold value change condition table 323 is a data table whichdefines conditions whereby the position threshold value and the timethreshold value are changed. FIG. 5 shows an example of the dataconfiguration of the threshold value change condition table 323. Asshown in FIG. 5, a threshold value change condition 323 a and athreshold value change amount 323 b are stored in the threshold valuechange condition table 323 while being associated with each other.Condition values for the number of satellites, the PDOP value, and theAPR average value are stored as the change condition 323 a. Thereception environment is likely to be the open-sky environment when theAPR average value is small, and is likely to be the multipathenvironment when the APR average value is large, as described above.Therefore, the threshold value of the APR average value is decreasedwhen the APR average value is small by setting the change amount to be anegative value, and is increased when the APR average value is large bysetting the change amount to be a positive value. The positioningaccuracy generally increases as the PDOP value decreases. Therefore, thethreshold value of the PDOP value is decreased when the PDOP value islarge by setting the change amount to be a negative value. Thepositioning accuracy generally increases as the number of satellitesincreases (i.e., the PDOP value decreases). Therefore, the thresholdvalue of the number of satellites is decreased when the number ofsatellites is large by setting the change amount to be a negative value.

The RAM 33 is used as a work area for the CPU 31, and temporarily storesa program and data read from the ROM 32, results of calculationsperformed by the CPU 31 based on various programs, and the like. FIG. 6shows an example of the configuration of the RAM 33. As shown in FIG. 6,the RAM 33 stores satellite position data 331, satellite set data 332,and positioning result data 333.

The satellite set data 331 is data relating to the position of a GPSsatellite acquired in each positioning process. FIG. 7 shows an exampleof the data configuration of the satellite position data 331. As shownin FIG. 7, a satellite position 331 b calculated based on the GPSsatellite signal is stored as the satellite position data 331corresponding to each GPS satellite 331 a acquired.

The satellite set data 332 is data relating to the satellite setselected in each positioning process. FIG. 8 shows an example of thedata configuration of the satellite set data 332. As shown in FIG. 8, aGPS satellite 332 b included in the selected satellite set, a presentposition candidate 332 c, a time error candidate 332 d, a number ofsatellites 332 e, a PDOP value 332 f, and an APR value 332 g are storedas the satellite set data 332 corresponding to each satellite set 332 aselected.

The positioning result data 333 is data relating to calculation resultsof each positioning process. FIG. 9 shows an example of the dataconfiguration of the positioning result data 333. As shown in FIG. 9, apositioning time 333 a, a selected satellite set 333 b, a locatedposition 333 c, a time error 333 d, a number of satellites 333 e, a PDOPvalue 333 f, and an APR average value 333 g are stored as thepositioning result data 333 corresponding to each positioning processfrom the start of positioning.

The present count values of the position counter and the time counterare stored as counter data 334. The present position threshold value andthe present time threshold value are stored as data 335.

The host CPU 40 controls each section of the portable telephone 1 basedon various programs such as a system program stored in the ROM 43.Specifically, the host CPU 40 mainly implements a telephone callfunction, and performs a process for implementing various functionsincluding a navigation function such as causing the display section 42to display a navigation screen in which the present position of theportable telephone 1 input from the baseband process circuit section 30is plotted on a map.

The operation section 41 is an input device including an operation key,a button switch, and the like. The operation section 41 outputs anoperation signal corresponding to the operation of the user to the hostCPU 40. Various instructions such as a positioning start/finishinstruction are input by operating the operation section 41. The displaysection 42 is a display device such as a liquid crystal display (LCD).The display section 42 displays a display screen (e.g., navigationscreen and time information) based on a display signal input from thehost CPU 40.

The ROM 43 stores a system program which causes the host CPU 40 tocontrol the portable telephone 1, a program and data necessary forimplementing a navigation function, and the like. The RAM 44 is used asa work area for the host CPU 40. The RAM 44 temporarily stores a programand data read from the ROM 43, data input from the operation section 41,results of calculations performed by the host CPU 40 based on variousprograms, and the like.

The portable telephone antenna 50 is an antenna which transmits andreceives a portable telephone radio signal between the portabletelephone 1 and a radio base station installed by a communicationservice provider of the portable telephone 1. The portable telephonewireless communication circuit section 60 is a portable telephonecommunication circuit section which includes an RF conversion circuit, abaseband process circuit, and the like, and transmits and receives aradio signal under control of the host CPU 40.

Process flow

FIG. 10 is a flowchart illustrative of the flow of the baseband process.The baseband process is implemented by causing the CPU 31 to execute thebaseband process program 321. A digital IF signal obtained bydown-converting an RF signal received by the GPS antenna 10 into an IFsignal by the RF receiver circuit section 21 is input to the basebandprocess circuit section 30 before the baseband process.

As shown in FIG. 10, the CPU 31 clears the position counter and the timecounter to zero as an initial setting (step A1). The CPU 31 thenperforms a positioning calculation process to calculate the presentposition P and the time error T (step A3).

FIG. 11 is a flowchart illustrative of the flow of the positioningcalculation process. As shown in FIG. 11, the CPU 31 calculatessatellite information (including the position) relating to each GPSsatellite based on the acquired GPS satellite signal (step B1). The CPU31 selects satellite sets made up of four or more GPS satellites basedon the acquired satellite signals (step B3), and performs a loop Aprocess on each satellite set selected.

In the loop A, the CPU 31 calculates the present position candidate (forthe position of the portable telephone 1) and the time error candidateby performing positioning calculations using a least-square method orthe like based on the position of each GPS satellite of the targetsatellite set (step B5). The CPU 31 calculates the number of GPSsatellites (number of satellites) included in the target satellite set(step B7). The CPU 31 calculates the PDOP value of the target satelliteset based on the calculated present position candidate (step B9), andthen calculates the APR value (step B11). The loop A is thus performed.

When the CPU 31 has performed the loop A process on all satellite sets,the CPU 31 calculates the APR average value of each satellite set (stepB13). The CPU 31 performs an evaluation process which evaluates eachsatellite set using the PDOP value and the like (step B15). The CPU 31selects one satellite set based on the evaluation results. The CPU 31determines the present position candidate corresponding to the selectedsatellite set to be the present located position, and determines thetime error candidate corresponding to the selected satellite set to bethe present time error (step B17). The CPU 31 thus completes thepositioning calculation process.

After completion of the positioning calculation process, the CPU 31performs a count process (step A5).

FIG. 12 is a flowchart illustrative of the flow of the count process. Asshown in FIG. 12, the CPU 31 calculates the difference (positiondifference) ΔP between the preceding located position and the presentlocated position (step C1). When the calculated position difference ΔPsatisfies the count-up condition (i.e., equal to or less than a givenvalue) (step C3: YES), the CPU 31 increments the position counter by one(step C5). When the calculated position difference ΔP does not satisfythe count-up condition (step C3: NO), the CPU 31 clears the positioncounter to zero (step C7).

The CPU 31 calculates the difference (time difference) ΔT between thepreceding time error and the present time error (step C9). When thecalculated time difference ΔT satisfies the count-up condition (i.e.,equal to or less than a given value) (step C11: YES), the CPU 31increments the time counter by one (step C13). When the calculated timedifference ΔT does not satisfy the count-up condition (step C11: NO),the CPU 31 clears the time counter to zero (step C15). The CPU 31 thuscompletes the count process.

After completion of the count process, the CPU 31 performs a thresholdvalue change process (step A7).

FIG. 13 is a flowchart illustrative of the flow of the threshold valuechange process. As shown in FIG. 13, the CPU 31 sets the positionthreshold value and the time threshold value at a reference thresholdvalue “3” as an initial setting (step D1). The CPU 31 changes theposition threshold value and the time threshold value based on thenumber of satellites referring to the threshold value change conditiontable 323 (step D3). The CPU 31 changes the position threshold value andthe time threshold value based on the PDOP value (step D5), and changesthe position threshold value and the time threshold value based on theAPR average value (step D7). The CPU 31 thus completes the thresholdvalue change process.

After completion of the threshold value change process, the CPU 31compares the position count value with the position threshold value, andcompares the time count value with the time threshold value. When theposition count value is less than the position threshold value (step A9:NO) or the time count value is less than the time threshold value (stepA11: NO), the CPU 31 returns to the step A3 and performs the nextpositioning. When the position count value is equal to or larger thanthe position threshold value (step A9: YES) and the time count value isequal to or larger than the time threshold value (step A11: YES), theCPU 31 determines the present position P to be the first locatedposition and outputs the first located position (step A13). The firstpositioning is thus completed.

After completion of the first positioning, the CPU 31 starts second orsubsequent positioning. Specifically, the CPU 31 performs thepositioning calculation process (see FIG. 11) (step A15), and outputsthe calculated present position P as the positioning result (step A17).The CPU 31 then determines whether or not to finish positioning. Whenthe CPU 31 has determined to continue positioning (step A19: NO), theCPU 31 returns to the step A15 and performs the next positioning. Whenthe CPU 31 has determined to finish positioning (step A19: YES), the CPU31 finishes the baseband process.

Modification

The embodiments to which the invention is applied have been describedabove. Note that embodiments to which the invention may be applied arenot limited to the above-described embodiments. Various modificationsand variations may be made without departing from the spirit and scopeof the invention.

(A) Decoding of Z-Count

For example, a variation in the time error T becomes almost zero even inthe multipath environment after the Z-count has been decoded. Therefore,when the Z-count has been decoded, the present position P may bedetermined to be and output as the located position without comparingthe count value with the threshold value.

(B) Host CPU

Some or all of the processes performed by the CPU 31 of the basebandprocess circuit section 30 may be performed by the host CPU 40 by meansof software.

(C) Positioning Device

The above embodiments have been described taking an example of aportable telephone which is an electronic instrument including apositioning device. Note that the invention may also be applied to otherelectronic instruments such as a portable navigation system, a carnavigation system, a personal digital assistant (PDA), and a wristwatch.

(D) Satellite Positioning System

The above embodiments have been described taking an example utilizingthe GPS. Note that the invention may also be applied to other satellitepositioning systems such as the global navigation satellite system(GLONASS).

(E) Recording Medium

A configuration may be employed in which the baseband process program321 is recorded on a recording medium such as a CD-ROM and installed inan electronic instrument such as a portable telephone.

Although only some embodiments of the invention have been described indetail above, those skilled in the art would readily appreciate thatmany modifications are possible in the embodiments without materiallydeparting from the novel teachings and advantages of the invention.Accordingly, such modifications are intended to be included within thescope of the invention.

1. A first output position calculation method that calculates a firstlocated position to be output after starting positioning when receivingsatellite signals transmitted from positioning satellites and performingpresent position positioning calculations based on the receivedsatellite signals, the method comprising: executing a positioningprocess that performs positioning calculations based on the receivedsatellite signals to calculate a located position; changing a repetitiveexecution count of the positioning process; and determining a finallocated position calculated when the positioning process has beenexecuted in a number corresponding to the repetitive execution count tobe a first located position to be output, the executing of thepositioning process including: selecting satellite sets based on thereceived satellite signals, each of the satellite sets being acombination of satellites used for a present positioning process;calculating present position candidates corresponding to the respectiveselected satellite sets using the satellite signals from the satellitesincluded in the respective selected satellite sets; calculating APRvalues of the respective selected satellite sets, the APR value beingthe sum of the square of the difference between 1) a pseudo-range and 2)an approximate distance of a target satellite of a target satellite set,the approximate distance being a distance between the target satelliteand the present position candidate of the target satellite set;calculating an APR average value of the present positioning process byaveraging the APR values of the respective satellite sets; selecting apresent position candidate from the present position candidatescorresponding to the respective satellite sets and determining theselected present position candidate to be a located position determinedby the present positioning process; and the changing of the repetitiveexecution count including changing the repetitive execution count basedon the APR average value.
 2. The first output position calculationmethod as defined in claim 1, the changing of the repetitive executioncount including changing the repetitive execution count based on the APRaverage value calculated by the present positioning process each timethe positioning process is executed.
 3. The first output positioncalculation method as defined in claim 1, the method further includingresetting and counting the repetitive execution count again when thedifference between the located position determined by the precedingpositioning process and the located position determined by the presentpositioning process does not satisfy a given short distance condition,and successively counting the repetitive execution count when thedifference between the located position determined by the precedingpositioning process and the located position determined by the presentpositioning process satisfies the given short distance condition.
 4. Thefirst output position calculation method as defined in claim 1, thecalculating of the present position candidate including calculating atime error using the satellite signals from the satellites included inthe target satellite set; the executing of the positioning processincluding determining the time error calculated when calculating thepresent position candidate to be a time error determined by the presentpositioning process; and the method further including resetting andcounting the repetitive execution count again when the differencebetween the time error determined by the preceding positioning processand the time error determined by the present positioning process doesnot satisfy a given approximation condition, and successively countingthe repetitive execution count when the difference between the timeerror determined by the preceding positioning process and the time errordetermined by the present positioning process satisfies the givenapproximation condition.
 5. The first output position calculation methodas defined in claim 1, the calculating of the present position candidateincluding calculating a time error using the satellite signals from thesatellites included in the target satellite set; the executing of thepositioning process including determining the time error calculated whencalculating the present position candidate selected as the locatedposition by the present positioning process to be a time errordetermined by the present positioning process; and the method furtherincluding resetting and counting the repetitive execution count againwhen 1) the difference between the located position determined by thepreceding positioning process and the located position determined by thepresent positioning process does not satisfy a given short distancecondition or 2) the difference between the time error determined by thepreceding positioning process and the time error determined by thepresent positioning process does not satisfy a given approximationcondition, and successively counting the repetitive execution count whenthe difference between the located position determined by the precedingpositioning process and the located position determined by the presentpositioning process satisfies the given short distance condition and thedifference between the time error determined by the precedingpositioning process and the time error determined by the presentpositioning process satisfies the given approximation condition.
 6. Afirst output position calculation method comprising: selecting satellitesets, each of the satellite sets being a combination of satellites usedfor a present positioning process; calculating present positioncandidates corresponding to the respective satellite sets usingsatellite signals from the satellites included in the respectivesatellite sets; calculating APR values of the satellites of therespective satellite sets based on the present position candidates;calculating an APR average value of the present positioning process byaveraging the APR values of the respective satellite sets; selecting apresent position candidate from the present position candidatescorresponding to the respective satellite sets and determining theselected present position candidate to be a located position determinedby the present positioning process; changing a repetitive executioncount of the positioning process based on the APR average value; anddetermining a final located position calculated when the positioningprocess has been executed in a number corresponding to the repetitiveexecution count to be a first located position to be output.
 7. Acomputer-readable storage medium storing a program that causes acomputer to execute a first output position calculation method thatcalculates a first located position to be output after startingpositioning, the computer being included in a positioning device thatreceives satellite signals transmitted from positioning satellites andlocates a present position of the positioning device based on thereceived satellite signals, the first output position calculation methodcomprising: executing a positioning process that performs positioningcalculations based on the received satellite signals to calculate alocated position; changing a repetitive execution count of thepositioning process; and determining a final located position calculatedwhen the positioning process has been executed in a number correspondingto the repetitive execution count to be the first located position, theexecuting of the positioning process including: selecting satellite setsbased on the received satellite signals, each of the satellite setsbeing a combination of satellites used for a present positioningprocess; calculating present position candidates corresponding to therespective selected satellite sets using the satellite signals from thesatellites included in the respective selected satellite sets;calculating APR values of the respective selected satellite sets, theAPR value being the sum of the square of the difference between 1) apseudo-range and 2) an approximate distance of a target satellite of atarget satellite set, the approximate distance being a distance betweenthe target satellite and the present position candidate of the targetsatellite set; calculating an APR average value of the presentpositioning process by averaging the APR values of the respectivesatellite sets; selecting a present position candidate from the presentposition candidates corresponding to the respective satellite sets anddetermining the selected present position candidate to be a locatedposition determined by the present positioning process; and the changingof the repetitive execution count including changing the repetitiveexecution count based on the APR average value.
 8. A computer-readablestorage medium storing a program that causes a computer to execute afirst output position calculation method that calculates a first locatedposition to be output after starting positioning, the computer beingincluded in a positioning device that receives satellite signalstransmitted from positioning satellites and locates a present positionof the positioning device based on the received satellite signals, thefirst output position calculation method comprising: selecting satellitesets, each of the satellite sets being a combination of satellites usedfor a present positioning process; calculating present positioncandidates corresponding to the respective satellite sets usingsatellite signals from the satellites included in the respectivesatellite sets; calculating APR values of the satellites of therespective satellite sets based on the present position candidates;calculating an APR average value of the present positioning process byaveraging the APR values of the respective satellite sets; selecting apresent position candidate from the present position candidatescorresponding to the respective satellite sets and determining theselected present position candidate to be a located position determinedby the present positioning process; changing a repetitive executioncount of the positioning process based on the APR average value; anddetermining a final located position calculated when the positioningprocess has been executed in a number corresponding to the repetitiveexecution count to be the first located position.
 9. A positioningdevice that receives satellite signals transmitted from positioningsatellites and performs present position positioning calculations basedon the received satellite signals, the positioning device comprising: apositioning section that executes a positioning process that performspositioning calculations based on the received satellite signals tocalculate a located position; a repetitive execution count changesection that changes a repetitive execution count of the positioningprocess; and a first output position determination section thatdetermines a final located position calculated when the positioningsection has executed the positioning process in a number correspondingto the repetitive execution count to be the first located position, thepositioning section including: a satellite set selection section thatselects satellite sets based on the received satellite signals, each ofthe satellite sets being a combination of satellites used for a presentpositioning process; a present position candidate calculation sectionthat calculates present position candidates corresponding to therespective selected satellite sets using the satellite signals from thesatellites included in the respective selected satellite sets; an APRvalue calculation section that calculates APR values of the respectiveselected satellite sets, the APR value being the sum of the square ofthe difference between 1) a pseudo-range and 2) an approximate distanceof a target satellite of a target satellite set, the approximatedistance being a distance between the target satellite and the presentposition candidate of the target satellite set; an average valuecalculation section that calculates an APR average value of the presentpositioning process by averaging the APR values of the respectivesatellite sets; and a present located position selection section thatselects a present position candidate from the present positioncandidates corresponding to the respective satellite sets anddetermining the selected present position candidate to be a locatedposition determined by the present positioning process; and therepetitive execution count change section including an APR average valuereference count change section that changes the repetitive executioncount based on the APR average value calculated by the positioningsection.
 10. The positioning device as defined in claim 9, therepetitive execution count change section changing the repetitiveexecution count based on the APR average value calculated by the presentpositioning process each time the positioning section executes thepositioning process.
 11. The positioning device as defined in claim 9,the positioning device further including a repetitive execution countcounting section that resets and counts the repetitive execution countagain when the difference between the located position determined by thepreceding positioning process and the located position determined by thepresent positioning process does not satisfy a given short distancecondition, and successively counts the repetitive execution count whenthe difference between the located position determined by the precedingpositioning process and the located position determined by the presentpositioning process satisfies the given short distance condition. 12.The positioning device as defined in claim 9, the present positioncandidate calculation section calculating a time error using thesatellite signals from the satellites included in the target satelliteset; the positioning section including a present time errordetermination section that determines the time error calculated when thepresent position candidate selected by the present located positionselection section has been calculated by the present position candidatecalculation section to be a time error determined by the presentpositioning process; and the positioning device further including arepetitive execution count counting section that resets and counts therepetitive execution count again when the difference between the timeerror determined by the preceding positioning process and the time errordetermined by the present positioning process does not satisfy a givenapproximation condition, and successively counts the repetitiveexecution count when the difference between the time error determined bythe preceding positioning process and the time error determined by thepresent positioning process satisfies the given approximation condition.13. The positioning device as defined in claim 9, the present positioncandidate calculation section calculating a time error using thesatellite signals from the satellites included in the target satelliteset; the positioning section including present time error determinationsection that determines the time error calculated when the presentposition candidate selected by the present located position selectionsection has been calculated by the present position candidatecalculation section to be a time error determined by the presentpositioning process; and the positioning device further including arepetitive execution count counting section that resets and counts therepetitive execution count again when 1) the difference between thelocated position determined by the preceding positioning process and thelocated position determined by the present positioning process does notsatisfy a given short distance condition or 2) the difference betweenthe time error determined by the preceding positioning process and thetime error determined by the present positioning process does notsatisfy a given approximation condition, and successively counts therepetitive execution count when the difference between the locatedposition determined by the preceding positioning process and the locatedposition determined by the present positioning process satisfies thegiven short distance condition and the difference between the time errordetermined by the preceding positioning process and the time errordetermined by the present positioning process satisfies the givenapproximation condition.
 14. A positioning device comprising: asatellite set selection section that selects satellite sets, each of thesatellite sets being a combination of satellites used for a presentpositioning process; a present position candidate calculation sectionthat calculates present position candidates corresponding to therespective satellite sets using satellite signals from the satellitesincluded in the respective satellite sets; an APR value calculationsection that calculates APR values of the satellites of the respectivesatellite sets based on the present position candidates; an averagevalue calculation section that calculates an APR average value of thepresent positioning process by averaging the APR values of therespective satellite sets; a present located position selection sectionthat selects a present position candidate from the present positioncandidates corresponding to the respective satellite sets and determinesthe selected present position candidate to be a located positiondetermined by the present positioning process; an APR average valuereference count change section that changes a repetitive execution countof the positioning process based on the APR average value; and a firstoutput position determination section that determines a final locatedposition calculated when the positioning process has been executed in anumber corresponding to the repetitive execution count to be a firstlocated position to be output.
 15. An electronic instrument comprisingthe positioning device as defined in claim
 9. 16. An electronicinstrument comprising the positioning device as defined in claim 14.